680: Media Center Edition
Then there's the model 680, which was more specifically designed to control a Microsoft Media Center PC. It's true that the layout resembles that of the Microsoft remote control. This is advantageous only if you use your Media Center in the living room associated with a display. As soon as you add other devices, like a satellite / DTV box or Home Theater system, you'll do better to choose another model. In fact, all the other remote controls in the line can also control a Media Center, with a different button layout. The features and price are the same as for the 688.
675/6: Media Chic
Then, we have the sports version (the 676 in the U.S and the 675 in Europe). The arrangement of the buttons is the same as on the 680, and so is the price (a little less expensive in Europe, by 20 euros), and so it's only a matter of looks. With its swappable color panels, it's aimed at fans of the Media Center who want to harmonize the colors of their environment.
655/9: Lowest On The List
Finally, there's the entry level model, the 655 in Europe and the 659 in the US. We can't really recommend it because it doesn't have the very practical central touchpad. At $149 or 99 euros, its price is too close to the model above to make it really interesting. If you're going to buy a universal remote and invest effort in programming it, you might as well get a little pleasure out of it.